Specifications

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Cisco Nexus 3000 Series NX-OS Unicast Routing Configuration Guide, Release 5.0(3)U2(2)
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Chapter 12 Managing the Unicast RIB and FIB
Information About the Unicast RIB and FIB
The unicast RIB maintains the routing table with directly connected routes, static routes, and routes
learned from dynamic unicast routing protocols. The unicast RIB also collects adjacency information
from sources such as the Address Resolution Protocol (ARP). The unicast RIB determines the best next
hop for a given route and populates the unicast forwarding information base (FIBs) by using the services
of the unicast FIB distribution module (FDM).
Each dynamic routing protocol must update the unicast RIB for any route that has timed out. The unicast
RIB then deletes that route and recalculates the best next hop for that route (if an alternate path is
available).
This section includes the following topics:
• Layer 3 Consistency Checker, page 12-2
• FIB Tables, page 12-2
• Virtualization Support, page 12-2
Layer 3 Consistency Checker
In rare instances, an inconsistency can occur between the unicast RIB and the FIB on each module. Cisco
NX-OS supports the Layer 3 consistency checker. This feature detects inconsistencies between the
unicast IPv4 RIB and the FIB on each interface module. Inconsistencies include the following:
• Missing prefix
• Extra prefix
• Wrong next-hop address
• Incorrect Layer 2 rewrite string in the ARP or neighbor discovery (ND) cache
The Layer 3 consistency checker compares the FIB entries to the latest adjacency information from the
Adjacency Manager (AM) and logs any inconsistencies. The consistency checker then compares the
unicast RIB prefixes to the module FIB and logs any inconsistencies. See the “Triggering the Layer 3
Consistency Checker” section on page 12-7.
You can then manually clear any inconsistencies. See the “Clearing Forwarding Information in the FIB”
section on page 12-8.
FIB Tables
The hardware provides two tables, a TCAM table and a Hash table. The TCAM table is shared between
the longest prefix match (LPM) route and the /32 unicast route. The Hash table is shared between the /32
unicast entries and the multicast entries. Each table has approximately 8000 routes.
Virtualization Support
The Unicast RIB and FIB support Virtual Routing and Forwarding instances (VRFs). By default, Cisco
NX-OS places you in the default VRF unless you specifically configure another VRF. For more
information, see Chapter 11, “Configuring Layer 3 Virtualization.”